Modern mobile communication devices comprise an impedance matching circuit for the impedance matching of the impedance of an antenna to the impedance of a signal path or to the impedance of downstream stages of the mobile communication device. In order to be able to effectively match the impedance, it is necessary to determine the actual matching. One measure of the actual matching is the reflection coefficient Γ or the voltage standing wave ratio (VSWR), which is dependent on the reflection coefficient. The reflection coefficient Γ is the quotient of power propagating in the forward direction and reflected power.
One known detector circuit from Maxim, the circuit MAX 2016, comprises a circulator, via which a reflected signal is coupled out from the signal path and fed to a logarithmic detector. At the same time, the signal propagating in the forward direction is fed to an amplifier via a second logarithmic detector. The respectively logarithmically amplified signals are fed to the two inputs of a subtractor. The subtractor subtracts the logarithmically amplified signals. A logarithmically amplified signal should be understood to mean a signal which is substantially proportional to a logarithm (e.g., the natural algorithm) of the original signal. The difference between logarithmically amplified signals then corresponds—in accordance with the addition theorem of the exponential function—to the quotient of the original signals. The output of the subtractor therefore yields a measure that is substantially proportional to the reflection coefficient Γ.